The present invention relates to a magnetic recording and reproducing apparatus for recording and reproducing the color television signal including VIR (Vertical Interval Reference) signal.
In the case of the color television signal transmission in VHF and UHF channels, VIR signal is inserted in the 19-th horizontal scanning cycle or period (according to the FCC standards) of each field as shown in FIG. 1 so that a repeater station may correct transmission distortions in amplitude and/or phase of the color television signal. Recently in the U.S.A. color television receivers have been produced which may control a color saturation and phase of color signal in reference to the VIR signal.
When the color television signal including VIR signal is recorded and reproduced by a video tape recorder, variations in amplitude and phase of VIR signal result because of the reasons to be described below so that the correction of transmission distortions cannot be attained, thus resulting in deviations in saturation and hue.
The distortion problem of VIR signal occurs in the so-called low-frequency conversion and helical scanning type color television signal recording and reproducing apparatus wherein the luminance signal is phase modulated and the carrier color signal is converted into the low-frequency carrier color signal and is superposed on or combined with the phase modulated luminance signal and wherein the guard bands between the adjacent recording tracks are eliminated. Since there exist no guard bands, cross-talk occurs between the adjacent tracks due to tracking errors and is mixed with the signal reproduced from the main track, thus causing interference. In order to minimize cross-talk, the head azimuth angle (for instance .+-.6.degree.) is varied at the adjacent tracks. Then cross-talk may be reduced by a degree corresponding to the azimuth loss. This is the reason why the azimuth recording system is employed in the guard-band-less type color television signal recording and reproducing apparatus.
In general, the shorter the wavelength, the higher the azimuth loss becomes. For instance, the azimuth loss is high when the luminance signal is phase or frequency modulated, but the azimuth loss is low when the carrier color signal is converted into a low-frequency of the order of hundreds kilohertz because the wavelength becomes longer. In order to eliminate cross-talk between the adjacent tracks (to be referred to as "adjacent cross-talk" for brevity in this specification), there has been proposed a system wherein the carrier color signals are recorded in the adjacent tracks in frequency interlace relationship as shown in FIG. 4 (wherein the frequency spectrum of the carrier color signal recorded in the main track is shown in full line while that of the carrier color signal recorded in the adjacent track in broken lines) and in the playback mode only the main signal is separated from the carrier color signal through a comb filter including a delay line for delaying the carrier color signal for a time equal to one horizontal scanning cycle or period.
Because of the relationship between the delayed and not-delayed carrier color signals, the main signals are added together to cancel cross-talk. However, the chroma reference signal of VIR signal is inserted only in one horizontal scanning cycle or period so that the color carrier signal has no VIR signal in the preceding horizontal scanning cycle or period (although in some cases VIT or test signal is inserted between the 16-th and 18-th horizontal scanning cycles or periods). Therefore the variations in amplitude and/or phase result in comb filter due to the chroma reference signals recorded in the adjacent tracks. As compared with the case where there is no adverse effect due to cross-talk, the amplitude drops by 6 dB.
Furthermore, if VIT signal is inserted in the preceding horizontal scanning cycle or period, it is added to that in the succeeding cycle so that wide variations in amplitude and phase result depending upon the contents of VIT signal. As a result, a color television receiver with VIR control cannot reproduce the correct saturation and hue.
The color television signal recording and reproducing apparatus wherein the recording tracks are spaced apart from each other by guard bands, is provided with a comb filter in order to improve the signal-to-noise ratio (S/N) and eliminate cross-color. Therefore when VIR signal is received, the saturation varies by 6 dB. When VIR and VIT signals are simultaneously received, both the amplitude and phase vary over a wide range so that the correct picture cannot be reproduced.